[PATCH] net/virtio-user: fix used ring address calculation

[Maxime Coquelin]

This patch fixes the used ring address calculation, to
avoid Vhost-vDPA backends (such as VDUSE) to fail while
trying to translate it.

Fixes: 666ef294ddf7 ("net/virtio-user: share descriptor IOVA to backend")
Cc: stable at dpdk.org

Reported-by: Adrian Moreno <amorenoz at redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
 drivers/net/virtio/virtio_user/virtio_user_dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c
index 187f81b066..7789f337f6 100644
--- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
+++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
@@ -149,7 +149,8 @@ virtio_user_kick_queue(struct virtio_user_dev *dev, uint32_t queue_sel)
 	} else {
 		desc_addr = vring->desc_iova;
 		avail_addr = desc_addr + vring->num * sizeof(struct vring_desc);
-		used_addr = RTE_ALIGN_CEIL((uintptr_t)(&vring->avail->ring[vring->num]),
+		used_addr = RTE_ALIGN_CEIL(avail_addr + offsetof(struct vring_avail,
+						ring[vring->num]),
 					   VIRTIO_VRING_ALIGN);
 
 		addr.desc_user_addr = desc_addr;
-- 
2.50.1